1. Field of the Invention
The present invention relates to a scroll compressor in which a fixed scroll and an orbiting scroll whose scroll laps rise from an end plate are meshed with each other to form a compression chamber therebetween, and when the orbiting scroll is turned along a circular orbit while restraining rotation by a rotation-restricting mechanism, the compression chamber moves while changing its volume, thereby carrying out suction, compression and discharge operations.
2. Description of the Related Art
In conventional scroll compressors of this type, both scroll laps forming a fixed scroll and an orbiting scroll are formed of involute curves which are involutes of a circle having a constant radius in many cases.
In some scroll compressors, thicknesses of portions or entire scroll laps of the fixed scroll and orbiting scroll are varied from centers of the scrolls toward the outer sides (see patent document 1 for example).
In some scroll compressors, a position of an orbiting scroll having asymmetric lap shape which is wound by one turn from outside of a scroll groove is increased in height by one step to form a stepped groove, a center of cylinder enters the stepped groove from an end plate surface, the scroll compressor is provided with a turning bearing having an axis in a region which is set from the groove step wall surface and the center of the scroll shape, a fixed lap of the fixed scroll also comprises a stepped lap so that it meshes with the stepped groove and a compression chamber can be formed (see patent document 2 for example).
FIG. 6 shows a conventional scroll compressor described in patent document 1. As shown in FIG. 6, in a scroll fluid machine in which one of scroll members allows the other scroll member to turn, thereby expanding or compressing fluid, the thickness of a portion or entire shape of a scroll body 22b of a scroll member 22 is increased or reduced from its center toward the outer side.
(Patent Document 1)
Japanese Patent Application Laid-open No.H11-264387
(Patent Document 2)
Japanese Patent Application Laid-open No.2000-329079
However, in the case of the conventional structure in which both the scroll laps forming the fixed scroll and the orbiting scroll are formed of involute curves which are involutes of a circle having a constant radius, if a basic circle radius a, an involute angle (the number of windings) of the scroll, thickness t and height h of the scroll lap are determined, a degree of freedom with respect to the scroll shape is limited and a stroke volume and an incorporating volume ratio are determined uniquely and thus, the conventional structure has the following problems.
That is, in the case of a compressor for freezing which is operated under a condition in which a ratio between a suction pressure and a discharge pressure is great, the incorporating volume ratio must be great. In order to increase the incorporating volume ratio, however, the involute angle (the number of windings) must be increased and as a result, the outside shape is increased. If the involute angle (the number of windings) is increased while keeping the outside shape size and the height of the scroll lap are set constant, there is a problem that the thickness of the scroll lap is reduced, the strength is deteriorated, or the stroke volume is reduced.
As a known example in which the degree of freedom in design of incorporating compression ratio, the stroke volume, the thickness of the scroll lap is enhanced, there is one described in patent document 1. In this known example, thicknesses of portions or entire scroll laps of the fixed scroll and orbiting scroll are varied from centers of the scrolls toward outer sides. Therefore, the incorporating volume ratio is secured while reducing the outside shape, and the strength of the center is secured.
On the other hand, if the scroll lap of the fixed scroll is formed into an asymmetric lap shape in which the scroll lap is expanded to a winding end of the scroll lap of the orbiting scroll, the stroke volume can be increased and thus, the height of the scroll lap or the outer shape size can be reduced. The compression chamber formed on the side of an outer wall of the scroll lap of the orbiting scroll can minimize the heat-reception loss and the pressure loss in a suction process for enclosing working fluid. Therefore, the scroll compressor can be made compact, and the loss of working fluid in the suction process can be reduced.
However, working fluid in the compression chamber formed on the side of the outer wall of the scroll lap of the orbiting scroll and working fluid in the compression chamber formed on the side of the inner wall of the scroll lap of the orbiting scroll are compressed in a state in which a difference between both the working fluids is maintained. Thus, there is a problem that leakage loss between the compression chambers is generated during the compressing process.
In patent document 1, there is no concrete explanation concerning the idea for reducing the leakage loss during the compression process in terms of the asymmetric lap shape.
Concerning the asymmetric lap shape, to reduce the leakage loss during the compression process, patent document 2 provides a known compact scroll compressor having high efficiency. In this known example, the lap is formed into a staircase shape. With this, the leakage loss during compression can be reduced although the lap is asymmetric in shape.
However, because the lap is formed into the staircase shape, there is a problem that it is difficult to secure sealing properties between the laps of the staircase portions, the number of producing processes is increase, and cost thereof is increased.
The present invention has been accomplished to solve the above conventional problems, and it is an object of the invention to provide a compact and simple scroll compressor which can reduce a leakage loss during compression process of an asymmetric lap shape.